VBlank increments counter in memory

And changes palette based on that

test_gfx.asm

@@ -4,6 +4,7 @@
 
 
 .EQU PalNum $0000
+.EQU VBlankCount $0010
 
 .BANK 0 SLOT 0
 .org 0
@@ -13,17 +14,11 @@ VBlank:
 
     Set_A_8_XY_16
 
-    stz $2115
-    ldx #$0400 ;setup VRAM
-
-    ldx #$0400
-    stx $2116  ; VRAM address
-
-    lda PalNum
-    sta $2119
+    lda VBlankCount
+    ina
+    sta VBlankCount
 
     lda $4210 ; clear NMI flag
-
     rti
 
 .ENDS
@@ -72,8 +67,8 @@ Start:
     stz PalNum
 
     Load_Palette_Color $00, $00
-    Load_Palette_Color $00, $00
-    Load_Palette_Color $00, $00
+    Load_Palette_Color $00, $0f
+    Load_Palette_Color $00, $ff
     Load_Palette_Color $ff, $0a
 
     Set_Screen_Brightness %00001111
@@ -105,26 +100,31 @@ Start:
 mainloop:
 
     wai
-    wai
-    wai
-    wai
-    wai
-    wai
-    wai
-    wai
-    wai
-    wai
-    wai
-    wai
 
-    lda PalNum
-    clc
-    adc #$04
-    and #$1c
-    sta PalNum
+    lda VBlankCount
+    beq SetBack
+    sbc #$80
+    beq SetDifferent
 
     jmp mainloop
 
+SetBack:
+    Reset_Palette_Offset
+    Load_Palette_Color $00, $00
+    Load_Palette_Color $00, $0f
+    Load_Palette_Color $00, $ff
+    Load_Palette_Color $ff, $0a
+    jmp mainloop
+
+SetDifferent:
+    Reset_Palette_Offset
+    Load_Palette_Color $0f, $f0
+    Load_Palette_Color $00, $0f
+    Load_Palette_Color $0a, $00
+    Load_Palette_Color $00, $00
+    jmp mainloop
+
+
 .ENDS